Some new designs of wireless communication devices—such as smart phones, tablet computers, laptop computers, and routers—contain hardware and/or software elements that provide access to multiple wireless communication networks. For example, a wireless communication device can have more than one radio frequency communication circuits (often referred to as “RF chains”) for accessing one or more wireless local area networks (“WLANs”) and/or wireless wide area networks (“WWANs”). When multiple reception (“Rx”) and/or transmission (“Tx”) operations are implemented, or co-exist, on a wireless communication device, these operations may overlap and interfere with each other.
This operation interference may occur in a wireless communication device with one or more RF chains. In a wireless communication device with multiple RF chains, the antennas of the RF chains may be in close proximity to each other. This close proximity may cause one RF chain to desensitize or interfere with the ability of another during the concurrent use of the RF chains.
Receiver desensitization (“de-sense”), or degradation of receiver sensitivity, may result from noise interference from a nearby transmitter. In particular, when two radios are close together with one transmitting on the uplink and the other receiving on the downlink, the feedback from the transmitter may be picked by the receiver or otherwise interfere with reception of a weaker signal (e.g., from a distant base station). As a result, the received signals may become corrupted and difficult or impossible to decode. Further, feedback from the transmitter can be detected by a power monitor that measures the receive signal, which would cause the mobile device to falsely determine the presence of a base station. In particular, receiver de-sense may present a challenge in multi-radio devices, such as devices configured with multiple SIMs, due to the necessary proximity of transmitter and receiver.
Other problems can occur in a wireless communication device with multiple RF chains. When executing multiple concurrent Tx operations the transmissions may create a disruptive intermodulation product or a battery current limit problem. Tx signals of different, but close, frequencies may be transmitted concurrently. Since Tx signals produce sideband noise on either side of a carrier frequency, the sideband noise may be of a frequency that overlaps with the frequency of another Tx signal. The concurrent transmission of overlapping frequencies can result in unwanted amplitude modulation causing noise on those overlapping frequencies and making it more difficult for receivers to distinguish signals. The battery current limit problem results from the power demands on the battery to concurrently transmit signals. The battery may not be able to provide sufficient current to multiple Tx chains, resulting in weaker signals and battery drain.
In a wireless communication device with one RF chain, multiple operations may require the use of the same function of the RF chain at the same time. For example, if two Rx operations are occurring at the same time, only one operation can have access to the Rx potion of the RF chain (or “Rx chain”) at a time. This may result in a prolonged delay or cancellation of the Rx operation that does not get to use the Rx chain.